SIMPLE SEQUENCE REPEATS AND MUCOID CONVERSION IN MISMATCH REPAIR-DEFICIENT Pseudomonas aeruginosa

MOYANO AJ; SMANIA AM

San Miguel de Tucumán

Congreso; XLV Reunión Anual de la SAIB; 2009

In Pseudomonas aeruginosa (PA), the main pathway for mucoid conversion is mutagenesis of the mucA gene, frequently due to -1 bp deletions in a simple sequence repeat (SSR) of 5 Gs (G5-SSR ). We 426 have recently observed that this mucA mutation is particularly accentuated in Mismatch Repair System (MRS)-deficient cells grown in vitro. Here, we evaluated the role of G5-SSR in 426 conversion to mucoidy under a MRS-deficient background. Thus, mucA alleles were engineered with different contents of G:C SSRs, and tested for their effect on the mucoid conversion frequency and mucA mutational spectra in a mutS-deficient PA. Deletion of G5- SSR severely reduced the emergence frequency of mucoid 426 variants, with no preferential site of mutagenesis within mucA. Moreover, although mutagenesis in mucA was not totally removed, this was no longer the main pathway for mucoid conversion, suggesting that G5-SSR biased mutations towards mucA. 426 Mutagenesis in mucA was restored by the addition of a new SSR (C6- SSR ), and even synergistically increased when G5-SSR and C6- 431 426 SSR were present simultaneously, with mutations being restricted 431 to -1 bp deletions within any of both G:C SSRs. These results confirm a critical role for G5-SSR in mucA mutagenesis of MRS- 426 deficient cells, and shed light on the contribution of SSR-dependent hypermutability in PA mucoid conversion.